Have had oil leaking from my 89 4.2 for years; about a quarter to a half dollar size leak every week plus from the valve cover, which is normal. Not enough to do a tear down so I lived with it. Local parts guy swears by this stuff so I tried it. Three weeks later, no leaks. Not one drop of oil on the undercarraige. Totally dry. (White Shepherd Stop Leak & Conditioner, 8oz. by Universal Products, Baltimore, MD). A bit expensive in my area at $30.00 for 8 oz. retail, but it was worth it. You might find it for less. Just thought I'd share the results.